Fuel injection into the cylinders of an internal combustion engine is commonly controlled using a solenoid operated fuel injection control valve. Typically, a solenoid actuator is energized to move a control valve element in a first direction causing the beginning of an injection event and de-energized to allow the control valve element to move in an opposite direction causing an end to the injection event. Minimizing the packaging size of a solenoid operated fuel injection control valve continues to be an important objective in designing components capable of fitting within the packaging constraints of a variety of engines. Such packaging constraints are of particular concern when the solenoid operated control valve is mounted on a fuel injector body. An even greater challenge exists in designing a solenoid operated control valve which can be incorporated within the injector body close to an injector nozzle assembly while maintaining, or minimizing, the size of the injector and achieving the control valve response time necessary for effective control of injection metering and timing. More importantly, designing an actuator housing for the solenoid actuator to decrease flux dissipation into the housing for maximizing a stronger attractive force is still a problem that has not been alleviated.
Recent and upcoming legislation resulting from a concern to improve fuel economy and reduce emissions continues to place strict emissions standards on engine manufacturers. In order for new engines to meet these standards, it is necessary to produce fuel injection systems capable of achieving higher injection pressures, controlled injection rates and fast response while maintaining accurate and reliable control of fuel metering and injection timing functions. As a result, solenoid actuator assemblies are undergoing structural modifications which assist in achieving these objectives. However, these improvements often undesirably increase the size of the injector which must conform to overall size restrictions or packaging constraints dictated by the mounting arrangement on a particular engine.
A solenoid actuator includes a core which forms pole pieces for attracting an armature connected to the control valve element. The core may be formed of a laminated stack of plates, i.e. laminate stack assembly, which is often chosen because of increased core resistivity. A laminate stack assembly permits faster magnetization and demagnetization of the solenoid by breaking up eddy current paths thereby reducing eddy currents. Conventional E-type or shaped laminate stack assemblies include three legs positioned in an inner cavity of an actuator housing. The end, or traction, faces of the legs are positioned adjacent the armature. The cross sectional areas of the end faces play a major role in determining the traction, or attractive, force on the armature. Increasing the attractive force results in a desirable decrease in the response time of the actuator/control valve thereby providing greater control of fuel injection timing and metering.
Attempts have been made to provide the response time required in high speed, high pressure applications. For example, the attractive force of the stator assembly of the solenoid actuator assembly can be increased by increasing the surface area of the stator pole end faces thereby decreasing response time. The end face area is increased by sizing and shaping the stator assembly to occupy a maximum amount of the space in a surrounding housing. However, it has been determined that flux leakage into the housing is created due to the substantially small spacing formed between the stator assembly and the interior surface of the housing thereby adversely affecting the operation of the assembly.
U.S. Pat. No. 5,676,114 issued to Tarr et al. discloses a fuel injector including a hydraulically controlled nozzle valve assembly. A solenoid actuator is mounted in the injector body adjacent the nozzle assembly for controlling the flow of fuel from a control volume to thereby control movement of the nozzle valve element. The solenoid actuator includes an E-type laminate stack assembly positioned in a generally circular or oval shaped cavity formed in an actuator housing. The legs of the E-type laminate stack assembly are conventionally shaped with a rectangular cross section. However, it has been determined that the conventional E-shaped laminate stack assembly, having legs with a rectangular-shaped cross section, does not create the response time necessary in certain applications.
U.S. Pat. No. 4,962,871 issued to Reeves discloses a solenoid actuated valve which maximizes the electromagnetic field generated by a solenoid coil so as to minimize the response time of the valve moving from a closed position to an open position. The actuator includes a dynamic pole having a generally circular shaped outer surface conforming to the inner surface of an assembly body. Grooves are formed in the outer surface to provide a path for fluid flow. Also, a static pole is positioned adjacent the dynamic pole. A valve plunger extends through the dynamic pole and into a bore formed in, and extending completely through, the static pole. However, the dynamic pole is connected to, and movable with, a valve plunger. As a result, the size of the dynamic pole is minimized to increase response time. Importantly, both the static and dynamic poles are formed of solid magnetic material. Thus, Reeves does not relate to laminate core assemblies nor E-type core assemblies. Also, the reference is not directed to a compact housing for the actuator which is capable of eliminating flux leakage into the housing.
German Patent No. 1,045,546 issued to Ulrich and Russian Patent No. 1,035,648 issued to Mindeli et al. disclose E-shaped laminate stack assemblies having legs with rectangular-shaped cross sections. The end faces of various legs include recesses formed from laminate plates having a shorter length than the remaining plates. Neither of these references disclose a compact housing capable of reducing flux leakage from the laminate stack assembly.
Japanese Patent No. 03-142804 discloses an E-shaped magnetic core including outer legs having a triangular cross-sectional shape and a center leg having a circular shape. However, the cross sectional shapes of the legs are designed to fit a fixed magnetic flux distribution thereby realizing more uniform distribution of magnetic flux. This reference does not appear to suggest mounting the E-shaped core in a housing to obviate flux leakage nor shaping the core to conform to the housing.
Thus, there is a need for a compact solenoid actuator assembly for operating a control valve in a fuel system including a stator assembly located in a housing to maximize dimensions of stator pole faces and to minimize flux leakage into the housing.